Tape drives are expensive, time-consuming and unreliable.
Tape drives cost $350 to literally thousands;
Unless you have a dedicated file server with an attached tape library, you can't readily access data stored on your tape drives. Even then, you can't access it through the Web, only through your local network.
Retrieving versions across multiple tapes can be complicated, time consuming and unreliable.
You can back up your entire system using a tape drive, but recovery typically is an extremely cumbersome, time intensive and failure-prone process involving a matrix of tapes, files and versions.
Do you have a tape drive recovery service to call if your in-house backup solution fails? How much do they charge?